The Sealy Library has numerous books on cartoons and cartoonists. Below are several subject headings to use in order to help retrieve relevant books.
American Wit and Humor
Caricatures and Cartoons
Editorial Cartoons
Political Cartoons
World politics Caricatures and cartoons
You can narrow these searches down by resource in the drop down menu to the right of the search term. Once you have searched, you can click on "Filter My Results" on the right. Mouse over the criteria you want to limit by and click the box that appears. Then Click the green "Apply Filters" box that pops up under the filter criteria.
Besides looking for books specifically on cartoons, it may be worthwhile to find books covering the time period/topic you are researching. For example, the multi-volume series entitled 20th Century available in the Library's Reference Section, contains articles on key historical events and topics of the 20th Century. Many articles contain political cartoons of the time depicting those events and topics.
Bok!: The 9.11 crisis in political cartoons by 
Editorial Cartoon Awards 1922-1997 by 
The ungentlemanly art; a history of American political cartoons by 
